Manufacture of alternating current rectifiers



Patented Dec. 23, 1941 v,MANUFACTURE case-e22 or ALTERNA'IING CURRENT RECTIFIE Leslie Ernest Thompson and Alexander Jenkins,

London, England, assignors, by mesne assignments, to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvama N Drawing.

Application September 6, 1939,

Serial No. 293,596. In Great Britain December Claims.

This invention relates to the manufacture of alternating current rectifiers of the kind comprising a rectifying .body or layer composed of or containing selenium, and has for its object to provide improvements in the manufacture of rectifiers of this character. v

As usually constructed, the rectifying element comprises a metal base plate or electrode upon the surface of which is formed in any suitable manner a relatively thin layer composed of or containing selenium in a crystalline or so-called metallic condition in which it is a relatively good conductor of electricity, a counter-electrode being provided in intimate contact with the surface of the layer and constituted for example by a metal film formed by any suitable process.

In this as in other dry surface contact rectifiers it is desirable that the resistance offered to the passage of current between the base plate or electrode and the counter-electrode should be as low as possible in one direction, termed the forward direction, and as high as possible in the other or reverse direction, and the present invention enables these conditions to be attained to an extent greater than has hitherto been possible by existing processes.

An essential feature in the manufacture of a rectifying element of the kind above described is a heat or other treatment for the purpose of converting the selenium from the amorphous condition into the desired crystalline or metallic condition, and according to the present invention, the element during or after this conversion treatment is arranged to be subjected to a treatment of an oxidising character for the purpose of producing on the surface of the selenium a modified condition or layer which co-operates with the counter-electrode to produce an improved rectifying action.

This treatment preferably consists in subjecting the rectifying element after the conversion treatment tc the action of a neutral, acid or alkaline liquid bath of an oxidising character, and it should be noted that the treatment does not involve the addition or presence of any other substances to or in the selenium, the reaction at the surface of the selenium layer involving the selenium only in a substantially pure state. Furthermore, although th treatment of the invention is, as above stated, of an oxidising character, the improvement in the rectifying action of the element may not require or be due to the formation of any permanent layer of selenium oxide, although it is probable that traces of this electrode, may be immersed in a bath of caustic soda, during which treatment a suitable voltage may be applied to the element in the reverse direction. The caustic soda bath preferably contains 25 grammes of caustic soda per litre of water, and is maintained at a temperature of approximately C. during the treatment.

Another suitable liquid bath which may be employed is an aqueous solution of sodium peroxide, both these baths being of an alkaline character.

A suitable neutral bath for the same purpose is an aqueous solution of hydrogen peroxide, while an aqueous solution of nitric acid of moderate concentration may also be successfully employed.

It will thus be seen that the invention may be carried into practice with a neutral, acid or alkaline bath.

In another process, according to the invention, the heat conversion treatment may be arranged to be carried out in a highly oxidising atmosphere such as relatively pure oxygen, which reacts with the surface of the selenium layer to produce the conditions above described, and in general it is found that the treatment of the invention enables the duration of the conversion or annealing treatment to be substantially reduced.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is:

1. The method for producing a selenium rectiiier which consists in subjecting the rectifier element after the conversion of the selenium to the metallic state to the action of a solution containing approximately 25 grammes of caustic soda per litre of water.

2. The method for producing a selenium rectifier which consists in subjecting the rectifier element after the conversion of the selenium to the metallic state to the action of a solution of caustic soda maintained at a temperature of approximately 60 C.

3. Th method for producing a selenium rectiiier which consists in subjecting the rectifier element after the conversion of the selenium to the metallic state to the action of a solution of caustic soda while a suitable voltage is applied to the element in the reverse direction.

4. The method for producing a selenium rectifier which consists in subjecting the rectifier element-after the conversion of the-selenium toand a suitable voltage being applied to the element in the reverse direction whilesubegcted the metallic state to the action of a solution containing approximately 25 grammes of. caustic soda per litre of water, said solution being maintainedat atemperature or approximately 60 C.

more: producing a selenium rectifler which consists 'in subjecting the rectifierelement after the conversion. of the selenium; .to

- the metallic state to the action or a solution containing approximately 25 grammes of caustic soda per litre oi. water, said solution being maintained at a temperature of approximately 60 C.

to the action of said solution.

LESLIE EENEs'r THOMPSQN. ALEXANDER JENxms.

D ISCLA I M'ER 2,266,922.-Leslie Ernest T ompson' and Alexander Jenkins London, England. ANUFACIURE 0F ALTERNATING CURRENT RECTIFIERS. Patent dated ecember 23, 1941. isclainier filed December 30, 1942, by the assignee,

Union Switch and Signal Company. Hereby disclaims the subje and 4. [Qflicial Gazette February 2, 1943.] 

